Coal, Oil, and Natural Gas

By editor

Glendive, Dawson County, Montana

Eastern Montana’s landscape offers more than the rugged silhouettes of badlands and the winding courses of the Yellowstone and Missouri rivers. Beneath the soil here lies a chronicle of fire and ancient life, recorded in the very rock and fuel that have shaped both the natural world and human industry. The red-colored rock and soil scattered throughout this region tell of subterranean fires that have burned intermittently for centuries, ignited by lightning strikes, spontaneous combustion, or exposure of coal seams by the relentless forces of erosion. These underground coal fires produce a dense, red-hued rock called clinker or scoria, a baked residue resulting from the intense heat of smoldering coal seams. The presence of clinker vividly demonstrates the slow transformation of coal over time and the dynamic processes still at work beneath the surface.

The coal itself belongs to the Fort Union Formation, a geological layer deposited during the Paleocene Epoch, roughly 55 to 65 million years ago. This epoch directly followed the mass extinction event that ended the reign of the dinosaurs, marking a world in transition. Rivers flowing from the nascent Rocky Mountains to the west and the Black Hills to the south carried abundant sediment and organic material into a shallow inland sea that once covered much of what is now the northern plains. These rivers traversed a subtropical coastal plain blanketed by sprawling swamps, where dense vegetation accumulated. Over time, peat from these swampy forests was buried beneath thick layers of sand, silt, and clay. The immense pressure and heat from these overlying layers compacted the peat into coal, while the sediment hardened into sandstone, siltstone, and mudstone.

The Fort Union Formation stretches beneath much of eastern Montana, western North Dakota, and northeastern Wyoming, containing an estimated 200 billion tons of coal. Geologists classify much of this coal as lignite--a softer, brownish variety of coal with lower energy content compared to bituminous or anthracite coals found elsewhere. The lignite seams are frequently found under the softer sedimentary rocks of the Fort Union Formation but occasionally surface in hill cuts or road excavations, exposing the dark layers to the open air and setting the stage for spontaneous ignition.

One might wonder how such fires start and persist through the centuries. Lightning strikes during dry periods can ignite exposed coal seams, as can wildfires sweeping across prairie grasses and shrublands. Additionally, when erosion exposes coal to the atmosphere, the oxidation process can generate enough heat to kindle a slow-burning fire. The burning of coal seams sometimes continues for decades or even centuries, as underground embers smolder far beneath the surface. The heat bakes the adjacent sedimentary rock, turning it into the red clinker that dots the landscape. This clinker serves as a geological record of both fire and the slow geological processes shaping the region.

The Fort Union Formation’s coal deposits are not merely geological curiosities; they have played a significant role in Montana’s industrial history. The American Fur Company established Fort Union in 1828 near the confluence of the Missouri and Yellowstone rivers. Though primarily a trading post, the fort’s location near these coal-rich lands would later gain importance as industrialization demanded new energy sources. By the late 19th and early 20th centuries, coal mining in eastern Montana became an important economic activity, fueling railroads and local industries.

Beneath this coal-rich terrain lies another geological treasure -- the Williston Basin. This expansive geological depression covers eastern Montana, extends into western North Dakota, and reaches up into southern Saskatchewan. The basin formed over hundreds of millions of years as the earth’s crust slowly subsided, creating a bowl-shaped depression where sediment accumulated to depths of up to 16,000 feet. These sediments included organic-rich deposits such as black shale, which, under conditions of heat and pressure, converted organic material into oil and natural gas.

The Williston Basin’s oil and natural gas reserves have long attracted prospectors and industrialists. The first commercial oil well in Montana was drilled in 1915, marking the beginning of an era that would transform the region’s economy and landscape. By the early 2000s, Montana’s oil production from the Williston Basin reached approximately 34 million barrels annually, with about 1,900 active producing wells reported by the Montana Board of Oil and Gas Conservation. Central to this production is the Bakken Formation, a dense shale layer within the basin that has emerged as one of North America’s most prolific oil-producing formations.

The Bakken shale’s potential was noted as early as the 1950s, but advances in horizontal drilling and hydraulic fracturing technology in the late 20th and early 21st centuries unlocked vast quantities of oil previously trapped in impermeable rock. This “shale revolution” revitalized local economies, brought new challenges, and reshaped the energy landscape of Montana and the surrounding region.

The naturalist and explorer Meriwether Lewis, who traversed these lands in 1805 during the famous Lewis and Clark Expedition, remarked upon the richness of the region’s resources. He wrote, “The coal beds are numerous and of various thickness, and the seams are often exposed along the river bluffs.” Lewis’s observation underscores the long-standing recognition of these fuels, even before their commercial exploitation.

While coal, oil, and natural gas have fueled human progress, they also remind us of the deep geological history embedded beneath our feet. The red clinker rocks scattered across the plains bear witness to ancient fires that may have burned long before human eyes first glimpsed this land. The vast coal seams and oil-bearing shales tell of lush Paleocene forests, great inland seas, and the slow, inexorable workings of sedimentation and heat that transformed organic matter into fuel. These processes unfold on timescales far beyond a human lifespan, inviting us to comprehend the natural world in its full temporal depth.

To walk the land around Glendive today is to stand atop layers of earth shaped by fire and water, by plant and animal life long vanished, and by forces both destructive and creative. The coal seams remind us of ancient forests that once thrived here, while the oil and gas deposits speak to the buried remains of microscopic organisms and vegetation that passed away millions of years ago. Together, they form a natural archive of transformation -- raw energy forged in the crucible of geologic time, now harnessed by human ingenuity.

See also

• Coal, Oil, and Natural Gas at Glendive, Dawson County
• Black Gold at Red Lodge, Carbon County
• A Fine Day for a Sail at Roy, Fergus County